Table of Contents

Assembling your own cart ROM image

Cartridge ROM images are burnt or flashed into ROM/flash chips. The file formats of the ROM images vary, but common formats are either raw binary dumps or the special .crt file format.

Most emulators can handle both of these formats, and hardware such as Retro Replay and 1541U with flash ROM can be used if you want to run your cartridge image on the real hardware without having a EPROM burner or other special hardware.

Suitable assemblers for cartridge ROM development

Most assemblers can be used to write your own cartridge ROM, but some are more suitable than others. For example, if you are planning to write a cartridge ROM that uses more than one ROM bank, you might want to use an assembler that, in one way or another, supports writing several segments that have the same start address. DreamAss deserves a special comment here since it has even more features in this direction. In addition to plain support of segments, it also has:

a pseudo op that returns the bank number of a symbol. this makes it very easy to build tables with bank/address for a cross-bank-call-api

the assembler can put functions into banks as they fit automatically, so you don't have to worry about memory layout.

Simple cartridge skeleton sources

Here are two small sources from the net that might help you to get up and running with an autostarting cartridge.

Copy a program from ROM to RAM and autostart it

This code is used to create a .crt ROM image which includes a copy of an executable program. When started, the code in the ROM copies the program to C64 RAM (from $0801) and executes it. The cart-reset-routine copies the “launcher” to $0400, executes it and somewhere near $0430 it says JMP $080b.

These CRTs will run in VICE and MMCR Bios 0.55 - source is in XA syntax